Event Driven server using Java NIO

Question

I'm trying to wrap my head around building an asynchronous (non blocking) HTTP server using java NIO. I presently have a threadpool implementation and would like to make it into Event Driven with single thread.

How exactly does an Event Driven server work? Do we still need threads?

I've been reading on Java channels, buffers and selectors. So after I create a serverSocketChannel and the selector and listen to requests, Do I need to hand over the request to other threads so that they can process them and serve the request. If so, how is it any different from a threadpool implementation.

And if I don't create more threads that can process the request, how can the same thread still keep listening to requests and process them. I'm talking SCALABLE, say 1 million requests in total and 1000 coming in concurrently.

Answer 1

I've been reading on Java channels, buffers and selectors. So after I create a serverSocketChannel and the selector and listen to requests, Do I need to hand over the request to other threads so that they can process them and serve the request.

No, the idea is that you process data as it is available, not necessarily using threads.

The complication comes out of the need to handle data as it comes . For instance, you might not get a full request at once. In that case, you need to buffer it somewhere until you have the full request, or process it piecemeal.

Once you have got the request, you need to send the response. Again, the whole response cannot normally be sent at once. You send as much as you can without blocking, then use the selector to wait until you can send more (or another event happens, such as another request coming in).